When the forest comes back to town

Audio 02:45

By: Florent Guignard

The trees are coming back to where they were cut. Urban forest projects are multiplying to support the return of nature to the city. In Paris, in 2019 we planted a primary, dense mini-forest, supposed to grow ten times faster, according to the method of Japanese botanist Miyawaki. Report 100 meters from the Paris ring road.

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Will urban forests save cities from global warming? Trees in town and in the ground, rather than in pots, however giant, “ between concrete and bitumen ” , as Maxime Le Forestier sang in the 1970s (his name announced the song). Initiatives and projects multiply as the suffocating threat of an urban thermometer flirting with 50 degrees Celsius approaches.

In Paris, pending the planting of four mini-forests announced by Anne Hidalgo, the mayor inaugurated in March 2019, between the Bois de Vincennes and the ring road, a “revolutionary” urban forest planted using the Miyawaki method. Akira Miyawaki, Japanese botanist, imagined the concept of primitive mini-forests, as they existed before human intervention, to restore degraded soils in record time.

Thirty times denser than a traditional forest

The plot measures only 700 square meters, and almost a year and a half after its planting, we went there in the company of Stéphane Hallaire, the president of ReforestAction, the company which participated in its creation and which promotes the method. Miyawaki. “ Instead of having one tree every eight to ten square meters, here we planted three trees per square meter. It is thirty times denser than a traditional forest. You cannot walk there, it is not a recreational place. It is a space returned to nature ” , and to all the biodiversity that composes it: animals, plants and fungi.

The density of Miyawaki forests induces two a priori contradictory phenomena. Symbiosis, first of all: the root systems help each other. Unity is strength. And then the competition: healthy competition. Natural selection. The trees thus grow much faster. Supporting example, Stéphane Hallaire stops in front of an already tall baby tree of 1.80m, whereas it measured only a few tens of centimeters a year ago. “ We planted this last year !” He enthuses. So we have extremely interesting growth rates. » In thirty years, we should obtain a forest that would have taken two centuries to grow.

" Significant temperature drops "

In addition to density, the Miyawaki method is based on diversity. “ In traditional forests, we will have two to five different tree species. Here, we have planted about twenty. " Twenty-three exactly, oak charm, which only grows in the region for centuries. Native species, capable of being more resilient in the face of disease, drought and heat waves.

The heat wave… this phenomenon more and more frequent and more and more feared by the inhabitants of the cities where the mineral dominates: stone, concrete, bitumen - all that is neither water nor vegetable to put it simply. Anything that retains heat, and prevents thermometers from dropping enough at night.

“ In the forest,” recalls Stéphane Hallaire, “ temperatures are two to eight degrees lower than those recorded in concrete areas. So that's what we expect here : significant temperature drops, in the forest, and in its immediate vicinity. "

Before leaving, we see a large burrow. No doubt that of a fox. “ This is good news for our forest,” says Stéphane Hallaire. Foxes hunt rabbits that could feed on the saplings that have been planted. " Nature returns to town and finds its balance.

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